1. Field of the Invention
The present invention relates generally to a scroll compressor suited for use in, for example, an air conditioner for business or domestic use and, more particularly, to a scroll compressor having well-balanced rotary elements.
2. Description of Related Art
FIG. 3 or FIG. 4 depicts a scroll compressor comprising orbiting and stationary scroll elements 1 and 2 in engagement with each other, a crankshaft 6 coupled with the orbiting scroll element 1, and an electric motor 3 for rotating the crankshaft 6 to orbit the orbiting scroll element 1 relative to the stationary scroll element 2. The crankshaft 6 is rotatably supported by a crank bearing 4 and an auxiliary bearing 5. A rotation prevention mechanism 7 is provided for preventing the orbiting scroll element 1 from rotating about its own axis while permitting it to undergo an orbiting motion of an orbiting radius of e.sub.0 relative to the stationary scroll element 2.
As shown in FIG. 5, during compression, the orbiting and stationary scroll elements 1 and 2 are held in line-contact with each other at a plurality of locations on internal and external surfaces thereof to define a plurality of crescent-shaped volume-variable working pockets therebetween. Each working pocket is gradually reduced in volume and increased in pressure as it approaches a center discharge port.
FIG. 6 schematically depicts how to balance a rotary machinery, while FIG. 7 schematically depicts a conventional method of balancing a scroll compressor.
As shown in FIGS. 6 and 7, the static balance and the dynamic balance have been calculated on the basis of the center of axis O of the crankshaft 6.
Static Balance: EQU F.sub.0 =m.sub.0 e.sub.0 .omega..sup.2, F.sub.b1 =m.sub.b1 e.sub.b1 .omega..sup.2, F.sub.b2 =m.sub.b2 e.sub.b2 .omega..sup.2 EQU Because F.sub.0 +F.sub.b2 =F.sub.b1, EQU m.sub.0 e.sub.0 +m.sub.b2 e.sub.b2 =m.sub.b1 e.sub.b1 ( 1)
Dynamic Balance: EQU Because F.sub.0 l.sub.1 =F.sub.b2 l.sub.2, EQU m.sub.0 e.sub.0 l.sub.1 =m.sub.b2 e.sub.b2 l.sub.2 ( 2)
where
m.sub.0 : off-centered eccentric mass,
e.sub.0 : amount of eccentricity between the center of axis O of the crankshaft 6 and the eccentric mass m.sub.0,
m.sub.b1 : mass of a main balance weight 8 (=orbiting radius),
m.sub.b2 : mass of an auxiliary balance weight 9,
e.sub.b1 : distance between the main balance weight and a center of axis O,
e.sub.b2 : distance between the auxiliary balance weight and the center of axis O,
l.sub.1 : distance between e.sub.0 and e.sub.b1, and
l.sub.2 : distance between e.sub.b1 and e.sub.b2.
Using Formulas (1) and (2) above, the values of m.sub.b1, m.sub.b2, e.sub.b1, and e.sub.b2 have been determined.
However, as disclosed in Japanese Laid-Open Patent Publication (unexamined) No. 59-215984, because the compression force acts as a rotating load in the scroll compressor, the crankshaft rotates while whirling within the crank bearing. In particular, the clearance between the crank bearing and the crankshaft is frequently set to a relatively large value in consideration of the clearance between mutually engaging blades of the orbiting and stationary scroll elements. Accordingly, the crankshaft actually rotates about it own axis while undergoing a whirling motion about the center of the crank bearing, thus producing an unbalanced exciting force. This force is one of the factors which enlarge vibrations of the rotary elements of the scroll compressor.